Technical Field
The present invention relates to Extreme Ultraviolet (EUV) pellicle fabrication, and more particularly to a mechanical isolation control for an EUV pellicle during EUV pellicle fabrication.
Description of the Related Art
During semiconductor wafer fabrication, extreme ultraviolet (EUV) light may be employed in, for example, a lithographic process to enable transfer of very small patterns (e.g., nanometer-scale patterns) from a mask to a semiconductor wafer. In EUV lithography, a pattern formed on an EUV lithographic mask (e.g., EUV reticle) may be transferred to a semiconductor wafer by reflecting EUV light off of portions of a reflective surface. A pellicle can be placed in front of the mask to, for example, avoid contamination of the mask and to prevent unwanted particles from reaching the mask surface, which may enable avoidance of alteration of the pattern to be transferred by the mask.
The fabrication of a pellicle (e.g., membrane) suitable for EUV imaging may be accomplished by selectively etching a silicon wafer including the pellicle material layer to create the desired free-standing membrane (e.g., pellicle). This subtractive method may employ wet processing methods and/or chemicals, and as such, the ultra-thin unsupported film (e.g., pellicle) needs to be able to withstand any forces exerted on its surface during the etch and rinse steps without breaking. In the case of EUV mask technology, as pellicles are conventionally very thin (e.g., ˜100 nm or less), managing the mechanical stability of the ultra-thin pellicle membrane in the presence of outside forces during fabrication is challenging, especially given the large surface area with respect to the thickness of an EUV pellicle. Outside forces may include, for example, mechanical vibrations (e.g., induced during manual pellicle handling, by moving parts that assist with controlled motorized translation), liquid and/or air pressure differentials on either side of the membrane (e.g., due to forced or natural convection), and/or capillary forces (e.g., due to meniscus formation at the liquid-air interface).